mlw wrote:
> Bruce Momjian wrote:
>
> >
> > OK, yes, sequential scan _can_ be as slow as index scan, but sometimes
> > it is faster. Can you provide reasoning why index scan should be
> > preferred, other than the admin created it, which I already addressed?
>
> If you have a choice between two or more sub-plans, similar in cost, say within
> 20% of one another. Choosing a plan which uses an index has a chance of
> improved performance if the estimates are wrong where as choosing the
> sequential scan will always have the full cost.
And the chance of reduced performance if the estimate was too low.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
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